Compressor unit and refrigerator using the unit

ABSTRACT

A compressor unit includes a compressor, an inverter for driving the compressor, and an over-current protective device for protecting the inverter against an output over-current. A control part controls the output voltage of the inverter when the compressor is started based on a ambient temperature detected by a temperature sensor so that the input current of the inverter does not exceed the working current value of the over-current protective device having temperature characteristics varying according to the ambient temperature. Thereby, a start torque can be increased by increasing the output voltage of the inverter without operating the over-current protective device when the compressor is stated at a low temperature when a start load is increased.

TECHNICAL FIELD

The present invention relates to a compressor unit and a refrigeratorusing the unit.

BACKGROUND ART

Conventionally, there has been a compressor unit that has been used in arefrigerator having refrigerant circuits. The compressor unit has acompressor, an inverter for driving the compressor, and an over-currentprotective device for protecting the inverter against an outputover-current. When the compressor is started, an inverter output voltageis set according to a working current value of the over-currentprotective device. That is, the inverter output voltage is set so thatan inverter output current does not exceed the working current value ofthe over-current protective device and so that a maximum starting torqueis gained. The over-current protective device, however, hascharacteristics in which a high ambient temperature decreases theworking current value and in which a low ambient temperature increasesthe working current value, as shown in FIG. 6. When the compressor isstarted at a low ambient temperature, accordingly, a problem is causedin that the inverter output voltage cannot be increased though there isroom for increase in the inverter output voltage resulting in increasein starting torque. When the compressor is started at a low temperature,in particular, a load is increased by increase in viscosity of oil inthe compressor, accumulation of liquid refrigerant or the like. In sucha case, therefore, the larger the driving torque is, the better.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a compressor unit bywhich a starting torque can be increased by increasing an output voltageof an inverter without operating an over-current protective device whena compressor is started at a low temperature when a start load isincreased, and to provide a refrigerator using the unit.

In order to achieve the object, the present invention provides acompressor unit comprising a compressor, an inverter for driving thecompressor, and an over-current protective device for protecting theinverter against an output over-current,

-   -   the compressor unit characterized in that a working current        value of the over-current protective device has temperature        characteristics varying according to an ambient temperature,    -   the compressor unit further comprising:    -   a temperature sensor for detecting the ambient temperature, and    -   a control part for controlling an output voltage of the inverter        on occasion of start of the compressor on basis of the ambient        temperature detected by the temperature sensor.

In accordance with the compressor unit having a configuration describedabove, in which the working current value of the over-current protectivedevice has the temperature characteristics varying according to theambient temperature, the compressor is started by an inverter outputvoltage such that an output current or an input current of the inverter,for example, which is compared with the working current value does notexceed the working current value corresponding to the ambienttemperature and thus the inverter output voltage can be increasedwithout activating the over-current protective device when thecompressor is started at a low temperature when a start load isincreased, so that the start of the compressor can be facilitated byincrease in a starting torque.

In a compressor unit of an embodiment, the control part determines theinverter output voltage on occasion of the start on basis of the ambienttemperature detected by the temperature sensor so that an output currentor an input current of the inverter is smaller than and in vicinity ofthe working current value of the over-current protective devicecorresponding to the ambient temperature detected by the temperaturesensor.

In accordance with the compressor unit of the embodiment, the inverteroutput voltage resulting in the output current or the input current ofthe inverter that is smaller than and in vicinity of the working currentvalue of the over-current protective device corresponding to the ambienttemperature detected by the temperature sensor is determined on basis ofthe ambient temperature detected by the temperature sensor. Therefore,the inverter output voltage on occasion of the start can be made as highas possible in accordance with the temperature characteristics of theworking current value of the over-current protective device.

In a compressor unit of an embodiment, the working current value of theover-current protective device has temperature characteristics in whichthe lower ambient temperature results in the larger working currentvalue and in which the higher ambient temperature results in the smallerworking current value, and

-   -   wherein the control part determines the inverter output voltage        on occasion of the start on basis of the ambient temperature        detected by the temperature sensor so that the lower the ambient        temperature detected by the temperature sensor is, the higher        the inverter output voltage on occasion of the start is and so        that the higher the ambient temperature detected by the        temperature sensor is, the lower the inverter output voltage on        occasion of the start is.

In accordance with the compressor unit of the embodiment, in which thelower ambient temperature results in the larger working current value ofthe over-current protective device and in which the higher ambienttemperature results in the smaller working current value of theover-current protective device, the lower the ambient temperaturedetected by the temperature sensor is, the higher the inverter outputvoltage on occasion of the start is made, and the higher the ambienttemperature detected by the temperature sensor is, the lower theinverter output voltage on occasion of the start is made. Thus theinverter output voltage on occasion of the start can be made as high aspossible in accordance with the temperature characteristics of theworking current value of the over-current protective device.

A refrigerator of the invention is characterized in that therefrigerator includes the compressor unit.

In accordance with the refrigerator having a configuration describedabove, the inverter output voltage can be increased without activatingthe over-current protective device on occasion of start at a lowtemperature when a start load is increased, so that the start of thecompressor can be facilitated by increase in a starting torque.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration of a compressor unit in accordancewith an embodiment of the invention;

FIG. 2 is a flowchart for illustrating operations of a control part ofthe compressor unit;

FIG. 3A and FIG. 3B are diagrams showing relations between ambienttemperatures and inverter outputs for determining an inverter outputvoltage on occasion of start of a compressor;

FIG. 4 is a diagram showing change in initial inverter output voltagewith lapse of time on occasion of start;

FIG. 5 is a diagram showing relations between operating frequencies andinverter output voltages; and

FIG. 6 is a diagram showing a temperature characteristic of workingcurrent value of an over-current protective device.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, a compressor unit of the invention and a refrigerator usingthe unit will be described in detail with reference to embodiments shownin the accompanying drawings.

FIG. 1 is a schematic configuration of a compressor unit for use in anair conditioner in accordance with an embodiment of the invention. Thecompressor unit has a rectifying circuit 1 to which an AC power supply(not shown) is connected, an inverter 2 for converting a DC voltage fromthe rectifying circuit 1 into an AC voltage, and a compressor 3 that isdriven by an output voltage from the inverter 2. An output terminal on apositive electrode side of the rectifying circuit 1 is connected to oneinput terminal of the inverter 2, and an output terminal on a negativeelectrode side of the rectifying circuit 1 is connected through acurrent shunt resistor 4 to the other input terminal of the inverter 2.Between both the output terminals of the rectifying circuit 1 isconnected a smoothing capacitor C. One end of the current shunt resistor4 on a side of the inverter 2 is connected through a resistor R, to oneinput terminal (on an anode side of a built-in light emitting diode) ofa photocoupler 5, and the other end of the current shunt resistor 4 on aside of the rectifying circuit 1 is connected to the other inputterminal (on a cathode side of the built-in light emitting diode) of thephotocoupler 5. Between both the input terminals of the photocoupler 5is connected a resistor R₂. One output terminal (on a collector side ofa built-in output transistor) of the photocoupler 5 is connected througha resistor R₃ to an input terminal of a control part 6, and the otheroutput terminal (on an emitter side of the built-in output transistor)of the photocoupler 5 is connected to a ground. A temperature sensor 7for detecting an ambient temperature is connected to an input terminalof the control part 6.

The control part 6 is composed of a microcomputer, an input-outputcircuit, and the like, and controls the output voltage of the inverter2. The shunt resistor 4, the photocoupler 5, and the resistors R₁ to R₄form an over-current protective device. When an input current for theinverter 2 becomes larger than a specified current while the compressor3 is operated by the inverter 2, a voltage across the current shuntresistor 4 is increased and the photocoupler 5 is turned on so thatactivation of the over-current protective device is notified to thecontrol part 2. Upon the activation of the over-current protectivedevice, the control part 2 turns off or reduces the output voltage ofthe inverter 2 and thereby prevents damage to the inverter 2 that mayresult from an output over-current. In the over-current protectivedevice configured as described above, working current values varyaccording to a temperature characteristic of the photocoupler 5. In thetemperature characteristic, as shown in FIG. 6, the lower an ambienttemperature is, the larger the working current value is; the higher theambient temperature is, the smaller the working current value is.

When the compressor 3 is started in the compressor unit configured asdescribed above, the control part 6 is activated to control the outputvoltage of the inverter 2 in accordance with a flowchart of FIG. 2. Uponstart of processing, in FIG. 2, an ambient temperature is detected bythe temperature sensor 7 in a step S1. The processing subsequently goesto a step S2, and an output voltage of the inverter 2 is selected inaccordance with the ambient temperature detected by the temperaturesensor 7. The processing then goes to a step S3, and the output voltageselected in the step S2 is outputted from the inverter 2 so as to drivethe compressor 3.

As the ambient temperature that is detected by the temperature sensor 7,a temperature of electrical equipment (not shown) is preferably detectedbut a temperature of outside air, a discharge pipe of the compressor 3,a heat exchanger, a radiating fin (for power transistors of theinverter) or the like may be used.

For the selection of the output voltage of the inverter 2 in the stepS2, an inverter output voltage that comes short of the working currentvalue is predetermined for each value of the ambient temperature onbasis of the temperature characteristic (shown in FIG. 6) of the workingcurrent value of the over-current protective device. That is, a relationbetween the inverter output voltages and the ambient temperatures ismade similar to the temperature characteristic of the working currentvalue of the over-current protective device. As shown in FIG. 3A, forexample, inverter output voltages may be determined so as to have alinear characteristic expressed by a linear expression approximate to acurve that shows a relation between the inverter output voltages and theambient temperatures or, as shown in FIG. 3B, an inverter output voltagemay be determined for every certain range of the temperature. Thus theinverter output voltage on occasion of the start is determined so thatthe input current for the inverter 2 is smaller than and in vicinity ofa working current value of the over-current protective devicecorresponding to the ambient temperature detected by the temperaturesensor 7.

The inverter output voltage that has been determined as described abovemay be outputted fully on occasion of the start of the compressor 3 or,as shown in FIG. 4, the output voltage may be increased gradually from avoltage lower than the determined inverter output voltage. A period oftime for which the initial voltage on occasion of the start of thecompressor 3 is outputted corresponds to a period of time that elapsesuntil a motor in the compressor 3 starts rotating and therefore may beshort, i.e., on the order of 100 msec. Extension of the period of timeaccording to circumstances is, however, effective for addressingincrease in oil viscosity, accumulation of liquid refrigerant or thelike on occasion of the start at low temperature.

On condition that an induction motor is used as the motor in thecompressor 3, a relation between the inverter output voltages andoperating frequencies has a linear characteristic (hereinbelow, referredto as VF characteristic) and an inverter output voltage is determined inaccordance with the VF characteristic. A change in the initial inverteroutput voltage in accordance with ambient temperatures causes adeviation from the VF characteristic. When an inverter output voltagecorresponding to a frequency f₁ at the start is changed, as shown inFIG. 5, among points a, b, and c in accordance with ambienttemperatures, the VF characteristic is switched to lines that link aninverter output voltage d corresponding to a frequency f₂ (outside anoperating range of the compressor 3) and the inverter output voltages a,b, and c corresponding to the frequency f₁. Thus the deviation thatoccurs between the inverter output voltages changed in accordance withinitial ambient temperatures and the VF characteristic is resolved.

Though the embodiment has been described with reference to thecompressor unit used for the air conditioner as a refrigerator, thecompressor unit of the invention may be used not only for airconditioners but for other refrigerators.

In the embodiment, the inverter input current detected by the shuntresistor 4 has a pulse shape, and the inverter output current that flowsfrom the three-phase AC voltage output inverter 2 to the compressor 3has an AC waveform. A peak value of the inverter output current isgenerally as large as a peak value of the inverter input current that isdetected by the shunt resistor 4 and that has the pulse shape. On basisof this principle, a peak value of a motor current can be found by theshunt resistor 4.

Though the shunt resistor 4 is provided on a negative electrode side ofthe inverter 2 in the embodiment, the shunt resistor may be provided ona positive electrode side of the inverter in order to detect theinverter input current. Though there is used the over-current protectivedevice composed of the shunt resistor 4, the photocoupler 5, and theresistors R₁ to R₄, the over-current protective device is not limitedthereto, and there may be used over-current protective devices havingother configurations or having different temperature characteristics ofworking current value. Over-current protection in the embodiment isperformed with use of the input current for the inverter 2 that isdetected by the shunt resistor 4; however, current detecting means maybe provided on the output side of the inverter and the protection may beperformed with use of the inverter output current detected by thecurrent detecting means. In the embodiment, the current is detected onthe negative electrode side because current measurement on the positiveelectrode side of the inverter increases a drift (floating) of thecurrent value and because current measurement on the output side of theinverter requires a complicated detecting circuit.

1. A compressor unit comprising a compressor, an inverter for drivingthe compressor, and an over-current protective device for protecting theinverter against an output over-current, the compressor unitcharacterized in that a working current value of the over-currentprotective device has temperature characteristics varying according toan ambient temperature, the compressor unit further comprising: atemperature sensor (for detecting the ambient temperature, and a controlpart for controlling an output voltage of the inverter on occasion ofstart of the compressor on basis of the ambient temperature detected bythe temperature sensor.
 2. A compressor unit as claimed in claim 1,wherein the control part determines the inverter output voltage onoccasion of the start on basis of the ambient temperature detected bythe temperature sensor so that an output current or an input current ofthe inverter is smaller than and in vicinity of the working currentvalue of the over-current protective device corresponding to the ambienttemperature detected by the temperature sensor.
 3. A compressor unit asclaimed in claim 1, wherein the working current value of theover-current protective device has temperature characteristics in whichthe lower ambient temperature results in the larger working currentvalue and in which the higher ambient temperature results in the smallerworking current value, and wherein the control part determines theinverter output voltage on occasion of the start on basis of the ambienttemperature detected by the temperature sensor so that the lower theambient temperature detected by the temperature sensor is, the higherthe inverter output voltage on occasion of the start is and so that thehigher the ambient temperature detected by the temperature sensor is,the lower the inverter output voltage on occasion of the start is.
 4. Arefrigerator including the compressor unit as claimed claim 1.